Rectifier



May 7 1930- H. c. RENTSCHLER ET AL 1,7 0 55- RECTIFIER Ffiled Dec. 151926 INVENTOR HARVEY C. RENTSCHLER WILLMM W.MERRY'MA ATTORNEY Patentedmay 27, 193% UNITED s'ra'rus PATENT; OFFICE HARVEY CLAYTON RENTSCHLER,OF EAST ORANGE, AND WILLIAM WALTER MERRY- MON, 01 GLEN RIDGE, NEWJERSEY, ASSIGNORS T0 WESTINGHOUSE LAMP OOH- PANY, A CORPORATION OFPENNSYLVANIA RECTIFIER Application filed December 15, 1926. Serial No.154,987.

This invention relates to electric discharge devices and morearticularly to glow discharge devices in w ich a rarefied gaseous atmosphere is employed. The invention is especially concerned with theproduction of a gaseous discharge rectifier of alternating currentemploying a monatomic gas such as argon, neon or helium or a mixture ofsuch gases and depending in part at least, upon the point-to-platedischarge principle and in part to the dissimilarity of the electrodematerials.

Considerable difficulty has hitherto been experienced in producingalternating current rectifiers of this type capable of operation at highpotentials, which depend on gas ionization for conduction of the currentand are independent of thermionic emission. Among the most seriousdifliculties is the disintegration or decomposition of the insulationsurrounding the oint electrode. This decomposition of the nsulationproduces a conducting film on the insulation, thus increasing theeffective area of the point electrode and causing back current to flowthrough the rectifier in considerable amounts.

Another source of trouble with this type of device is the disintegrationof the point electrodes, causing destruction of the electrodes andforming conducting de osits on the insulation, thus increasing the ackcurrent or causing electrical leakage between the electrodes. Ionbombardment of the interior surface of the envelope is also anobjectionable feature in such devices, resulting in the release of gasesfrom the walls of the envelope and contaminating the gaseous filling.-This contamination of the gaseous filling increases the starting andoperating potential of the device and produces a large increase in thepotential dr'op through the rectifier, often causing it to becomeentirely ino erative.

ne of the objects of the present invention is to produce a gaseousdischar e rectifier capable of supplying relatively high voltage directcurrent which will overcome the above mentioned difliculties and whichwill have a long life, uniform operating characteristics and a lowvoltage drop.

Another object is to produce such a device in which the discharge willbe substantially entirely in one direction, that is, in which the backcurrent will be suificiently small to be unobjectionable.

Another object is to provide an improved electrode construction and amethod of treating the electrode so as to reduce the back current in thedevice, due to impurities in the electrode to an unobjectionable degree.

Other objects and advantages will hereinafter appear.

We have found that when the anode of a pomt-to-plate discharge deviceutilizing a monatomic gas at suitable pressure is composed of carbon orgraphite properly isolated from its surrounding insulation and suitablydisposed with respect to the cathode and when the active cathode surfaceis formed of a suitable material and the residual gases and impuritiesthoroughly removed from the device and from the electrodes so that thecarbon or graphite anode is free from impurities and the device containsonly a pure inert gas, the discharge between the electrodes takes placealmost entirely in one direction even at high voltages.

The carbon or graphite anode, we have found, overcomes the diflicultieswhich heretofore have been experienced, due to disintegration of theanode in operation. The graphite, however, must be specially treated tocompletely remove all gases and impurities therefrom since otherwise theback current may be objectionabl high. The carbon or graphite anode shoud be as pure as is commercially obtainable andshould preferably betreated out after incorporation into and sealing off of the device byappropriate electrical treatment to complete the purification anddegasification thereof. We have found that the back current withgraphite electrodes is much smaller than with metal, so that for thesame degree of rectification it is possible to employ much largergraphite anodes than is possible with metallic anodes. In place of thecarbon anode, a metal such as thorium, uranium or titanium may beemployed.

The insulation adjacent the anode is disposed out of contact with theactive portion of the anode in such manner as to hinder the heating andconsequent decomposition of the insulation, due to the discharge and the1nsulation is so arranged as to preclude the formation of continuousconducting paths between the anode or the anode leads and such ortionsof the insulation as are ca able of Being rendered conductive either byssociation of the insulating material or deposition of the electrodematerial thereon.

The ion bombardment of the lnsulatmg portions of the device, such as thelnterior surface of the envelope, may be reduced to an inappreciableamount by employing argon as the gaseous filling. We have d1scoveredthat at the gas pressure necessar for operation of the device, that thedisc arge in argon is confined very closely to the space between theelectrodes and does not extend to any extent to the walls of the device.

Low starting and operating potential may be obtained by employingametallic getter, such as misch metal, on the cathode which serves notonly as a clean-up agent to remove gaseous impurities initially, butalso serves throughout the life of the device to maintain the gaseousfilling in a pure condition. The misch metal, moreover, forms an activesurface on the cathode of low cathode drop and thereby greatlyfacilitates the discharge.

In order that the invention may be more fully understood, reference willbe had to the accompanying drawing in which:

Fig. 1 is an elevation partly in section of a full wave rectifierembodying the present invention;

Fig. 2 is a diagrammatic arrangement of apparatus employed in treatingthe electrodes and developing the starting and operating characteristicsof the device;

Fig. 3 is a sectional view of the electrode assembly of a half waverectifier of slightly modified construction;

Fig. 4 is a further modification of a half wave rectifier.

The device shown in Fig. 1 comprises an envelope 1 containing a pair ofanodes 2 and 3, a cathode 4 and a filling of monatomic gases or amixture of gases such as argon, neon or helium. Argon, however, ispreferred since it causes the discharge to be restricted substantiallyto the interelectrode space, whereas with both the neon and helium at hih voltages, intense ion bombardment of t e glass envelope may takeplace.

The anodes'2 and 3 are preferably composed of carbon or graphite and arecarried y support wires 5 and 6, which also serve as current conductorsand are sealed in the press 7 of the device. In order to restrict thedischarge to the anodes 2 and 3, the support wires are enclosed in glassor quartz sleeves 8 and 9 and immediately adjacent the nodes both thesupport and the glass sleeves are protected by highly refractoryinsulating material, such as sleeves 10 and- 11 of lavite. Each of thelavite sleeves is provided intermediate its ends with a web 12 having aperforation 13 through which the support wire extends. One end of eachof the anodes 2 and 3 is threaded interiorly for attachment to thethreaded end 14 of the support wire. For a reason which will appear morefully hereinafter the anodes and their support wires are spaced a slightdistance from the interior surface of the lavite sleeve, and the webportion 12 of the lavite sleeve is spaced away from the end of the glassor quartz tubes. In order to maintain the parts accurately in concentrics aced relation the support wires 5 and 6 t rather closely in the boreof the glass or quartz sleeves 8 and 9 and the cylindrical lower portion15 of each of the lavite sleeves close ly engages the glass tubes.Intermediate their ends, each of the lavite sleeves is provided with a.circumferential groove 16 in which a wire 17 is wrapped and one or bothends of this wire Welded or otherwise suitabl secured to the supportwires 18 from w rich the cathode is supported. This is more clearly seenin Fig. 4.

The cathode 4 is of cylindrical shape and preferably formed of ironalthough molybdenum may also be used if desired.

The anodes 2 and 3 and the cathode 4 are provided with currentconducting leads 19, 20 and 21 connected to the terminals 22, 23 and 24respectively, of the base 25. A piece of misch metal 26 which forconvenience may be in the shape of a wire or ribbon, is secured to thecathode 4 in any desirable manner, such as welding, but as shown isretained in place by a strap 27 struck up from the surface of thecathode. The plate is treated out and the misch metal is vaporizedeither before or after the gaseous filling is introduced by highfrequency induction current. Starting tips or wires 28 may be secured tothe cathodeand the free ends brought into proximity to the end of eachof the anodes to get lower and'more uniform starting voltage during thelife of the rectifier.

The pressure of the gaseous filling depends upon the particular gas ormixture of gases used. For example, with argon the pressure ispreferably of the order of 5 mm. of mer-t cury, whereas with neon orhelium it is necessary to use a considerably higher pressure in order toobtain the requisite operating characteri'stics. In general, a gaspressure of from 2 to 10 mm. may be employed, depending upon the gasused and the current output impurities coming from the anode assemblyorfrom the cathode so that the tube will contain only pure inert gas.This may be The cathode 4 is first degasified and thus treated out durinthe high frequency flashing process whic vaporizes some of the mischmetal and renders the gas filling pure.

The anodes 2 and 3 are then best treated by passing a discharge throughthe device in i such manner as to heat the same, thus liberating the imurities and gases therefrom.

- Referring to igure'3, if the switch 34 is left open the condenser 32charges up from the v rectified current and on the reverse cycle whenthe anodes become negative, imposes a relatively high potential betweenthe anodes serving as a cathode and the cylinder or plate as anode, thusheating up the graphite anodes and liberating the gases and impuritiestherefrom. During all this time the misch metal on the late and thatwhich has been va orized, ta es up the impurities liberated rom theanode and maintains the gas pure. In some cases it may be necessary tothen operate the device with the load 33 in the circuit, causing asufiiciently heavy discharge to pass between the plate 4 and the anodesto va orize more of the misch metal from the p ate and thus furtherclean such impurities as have been liberated from the anodes during thetreatment before described.

If desired, in place of using the arrangement shown in Fig. 3 a highvoltage direct current discharge may be passed through the device insuch direction as to render the electrodes 2 and 3 negative and then ina reverse direction so as to make the electrode 4 the cathode.

The anodes 2 and 3 are spaced from the lavite sleeves a slight distanceso as to prevent the discharge from coming in contact with the laviteand decomposing the same. Referring to Fig. 1, for instance, if theanode 2 and the lavite sleeve 10 were in contact, the discharge at thepoint of contact between these two members would heat up the insulationand decompose the same with the formation of a metallic surface thereon,and causing the back discharge to be largely concentrated at this ointthus producing further heating and re notion of the insulatlon. In ashort time the entire insulator may be rendered conductive and insteadof having a small anode, the effective area of the electrode may includethe entire exterior surface of the insulator, thus very materiallyincreasing the back current and lowering the elficienc of the rectifier.By spacing the electrode an the insulator from each other, there islittle likelihood of the insulation decomposing under the discharge butshould such decomposition take place or should it become coated withcarbon volatilized from the anode, it will not be in electrical contactwith the graphite and hence will take no part in the discharge. Byspacing this insulator from both the anode and support wire, a long pathis created between the exterior surface of the insulator and the anodesupport wires so as to insure that there will be no electrical contacttherebetween. It will be noted that the web portion 12 of the insulatorforms on the under side thereof, what may be termed a shadow zone, sothat any carbon volatilized from the anode and moving outwardl therefromin straight lines cannot become eposited on the under side of the web.This zone at least, is therefore, fully protected from deposition ofconducting material and forms an insulating gap between the exteriorsurface of the insulator and the lead wire of the anode.

In Fig. 4 the graphite anode 35 is set below the surface of the laviteinsulator which construction it has been found, gives the effect of asmaller effective point for the electrode.

In Fig. 4 there is shown a construction which is suitable for lowervoltages. In this modification the construction is somewhat sim lifiedby reducing the degree of isolation of the anode and its insulation. Thelavite sleeve is maintained in position on the quartz or glass tube bythe expedient of screwing the anode tightly against the web portion ofthe insulator. A metal washer 37 is inserted between the lower end ofthe graphite and the web portion of the insulator, however, topreventactual contact of the graphite with the insulation. This contactis ob ectionable since the carbon apparently facilitates thereduction-of the refractory oxide of which the insulator is composed.

If still lower operating voltages are to be employed, that is, voltagesof from 100 to 150 volts, direct current output, the metal washer may beomitted and the graphite brought into actual contact with theinsulation. f

The misch metal serves through out the life of the device to maintainthe as in pure condition and the operating an starting characteristicsuniform, and due to its'presence on the surface of the cathode greatlyreduces the cathode drop and renders it possible to start the dischargeat low potentials. The spacing of the anode and cathode is not criticalandrby way of illustration, excellent results have been obtained,employing a cylindrical cathode of about one inch in diameter and oneand one-half inches long with the anodes dis (1 therein, adjacent thelower end thereo or if desired the anodes may extend well up within theinterior of the cathode Obviously manychanges and modifications may bemade in the construction of the device and we do not desire to be.limited exce 1: in accordance with the annexed claims.

10 at is claimed is:

1. An electric discharge device comprisingan envelope containing amonatomic gas, a cathode therein of large area and an anode ofrelatively small area, whereby a unidirec- 15 tionally electricdischarge may be obtained, said anode being composed of carbon in asubstantially pure and gas-free condition and a quantity of misch metalon said cathode for reducing the cathode resistance.

20 2. A gaseousdischarge rectifier comprising an envelope containing amonatomic gas at a pressure of from 2 to 10 millimeters, an anodecomposed of carbon and a cathode of large effective area having ametal-of the cerium group of rare earth metals disposed thereon.

. In testimony whereof, we have hereunto subscribed our names this 14thday of December, 1926. 1 30 HARVEY CLAYTON RENTSCHLER.

WlLI-IAI WALTER MERRYMON.

